The present invention relates to current meters and, in particular, is directed to current meters for simultaneously measuring horizontal and vertical components of a current relative to depth.
The need for the measurement of currents in oceanography and ocean engineering has resulted in the development of many different types of current meters. With respect to their use, current meters can be divided into two large groups. The first group comprises current meters that measure current as a function of time. These meters are either moored to the ocean bottom or move freely with the current as neutrally buoyant floats.
The moored meters use a variety of principles, the most widely employed principle being exemplified by the Savonius rotor-type meter. Electromagnetic meters, acoustic meters, meters that use hot film anemometry and meters that use the vortex shedding principle are also known. For example, U.S. Pat. No. 3,695,103 discloses a meter, fastened to the sea floor or river bed, which uses strain gauge sensing devices. The neutrally buoyant floats measure horizontal current by monitoring displacement or vertical current by counting the number of revolutions around a vertical axis in a fixed time period due to the vertical current.
The second group of current meters measures currents as a function of depth. This group can again be divided into two types. The first type which is most widely used is lowered from a ship by means of an oceanographic winch, thus giving a number of current versus depth values. The second type, which is not commonly used, is a free falling or rising meter which can measure horizontal currents only. U.S. Pat. Nos. 3,834,229 and 3,972,231 typify such types of current meters.
It is an important object of the present invention to introduce into the field of oceanography and ocean engineering a new type of current meter which is based on the measurement of acceleration due to the action of currents on an immersed unrestrained body.
It is another important object of the present invention to provide an improved current meter which can measure simultaneously both horizontal and vertical current components as a function of depth.
A further object of the invention is to provide a current meter which can measure substantially continuously, uninterrupted current profiles, i.e. profiles with a high vertical resolution for determining the magnitude of both horizontal and vertical current components and their direction of flow.
It is another object of the invention to provide a current meter which can measure water current with high sensitivity and resolution, i.e. the meter is sensitive to small current changes.
A further object of the present invention is to provide a free falling current meter which can measure ocean currents up to a depth of 6000 m.
It is another object of the invention to provide a simple, compact and lightweight current meter which can be operated by unskilled personnel without sophisticated equipment for deployment and retrieval but which can be manually deployed and retrieved.